The present invention relates to a combustor for a gas turbine and, more particularly, to a gas turbine combustor having an inner cylinder provided with a multiplicity of louvers and a plurality of air ports.
Generally, the inner cylinder of a gas turbine combustor is provided with a plurality of air ports for supplying combustion air, and a multiplicity of louvers for generating a thin layer of air along the inner surface of the inner cylinder. The air layer on the inner surface of the inner cylinder serves as a heat-insulating layer for protecting the wall of the inner cylinder from the hot combustion gas. In order to generate this air layer over the entire area of the inner surface of the cylinder so as to attain an effective cooling of the inner cylinder, it is necessary to densely arrange a multiplicity of small louvers defining air inlets in the wall of the inner cylinder.
The simplest method of forming the louvers in the inner cylinder is to form a multiplicity of arcuate slits in the cylindrical wall and to form a radial step between the wall portions at both sides of each arcuate slit by a relative radial deformation between these wall portions. The arcuate slits thus shaped into the form of louvers serve as air inlets for generating a layer of air flowing along the inner surface of the inner cylinder. This method of forming the louvers is comparatively simple but involves a problem that cracks are liable to occur in the wall at both ends of each louver. Namely, a considerably large thermal stress is generated in the inner cylinder due to temperature variation of the same during the operation of the gas turbine, and the stress is concentrated at the keen edges at both ends of each louver to cause cracks in such keen edges. If the cracks are developed and propagated to adjacent louvers or air ports, the inner cylinder of the combustor will be locally cut to allow a small piece or fragment to be separated from the wall of the inner cylinder. Such a small piece or fragment will be blown into the turbine which is connected to the downstream side of the combustor as viewed in the direction of flow of the gas to seriously damage the moving and stationary blades in the turbine. In order to avoid the cracking in the inner cylinder wall, therefore, it has been a common measure to renew the inner cylinder at a frequency of, for example, every two years.